test: Fix Pydantic v2 compatibility and comprehensive API testing

This commit migrates all models to Pydantic v2 and adds comprehensive
testing infrastructure for the news-engine-console backend.

Model Changes (Pydantic v2 Migration):
- Removed PyObjectId custom validators (v1 pattern incompatible with v2)
- Changed all model id fields from Optional[PyObjectId] to Optional[str]
- Replaced class Config with model_config = ConfigDict(populate_by_name=True)
- Updated User, Keyword, Pipeline, and Application models

Service Changes (ObjectId Handling):
- Added ObjectId to string conversion in all service methods before creating model instances
- Updated UserService: get_users(), get_user_by_id(), get_user_by_username()
- Updated KeywordService: 6 methods with ObjectId conversions
- Updated PipelineService: 8 methods with ObjectId conversions
- Updated ApplicationService: 6 methods with ObjectId conversions

Testing Infrastructure:
- Created comprehensive test_api.py (700+ lines) with 8 test suites:
  * Health check, Authentication, Users API, Keywords API, Pipelines API,
    Applications API, Monitoring API
- Created test_motor.py for debugging Motor async MongoDB connection
- Added Dockerfile for containerized deployment
- Created fix_objectid.py helper script for automated ObjectId conversion

Configuration Updates:
- Changed backend port from 8100 to 8101 (avoid conflict with pipeline_monitor)
- Made get_database() async for proper FastAPI dependency injection
- Updated DB_NAME from ai_writer_db to news_engine_console_db

Bug Fixes:
- Fixed environment variable override issue (system env > .env file)
- Fixed Pydantic v2 validator incompatibility causing TypeError
- Fixed list comprehension in bulk_create_keywords to properly convert ObjectIds

Test Results:
- All 8 test suites passing (100% success rate)
- Tested 37 API endpoints across all services
- No validation errors or ObjectId conversion issues

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

services/news-engine-console/backend/app/models/application.py

@@ -1,30 +1,29 @@
 from datetime import datetime
 from typing import Optional, List
-from pydantic import BaseModel, Field
-from bson import ObjectId
-
-
-class PyObjectId(ObjectId):
-    """Custom ObjectId type for Pydantic"""
-    @classmethod
-    def __get_validators__(cls):
-        yield cls.validate
-
-    @classmethod
-    def validate(cls, v):
-        if not ObjectId.is_valid(v):
-            raise ValueError("Invalid ObjectId")
-        return ObjectId(v)
-
-    @classmethod
-    def __get_pydantic_json_schema__(cls, field_schema):
-        field_schema.update(type="string")
+from pydantic import BaseModel, Field, ConfigDict
 
 
 class Application(BaseModel):
     """OAuth2 Application data model"""
 
-    id: Optional[PyObjectId] = Field(default=None, alias="_id")
+    model_config = ConfigDict(
+        populate_by_name=True,
+        json_schema_extra={
+            "example": {
+                "name": "News Frontend App",
+                "client_id": "news_app_12345",
+                "redirect_uris": [
+                    "http://localhost:3000/auth/callback",
+                    "https://news.example.com/auth/callback"
+                ],
+                "grant_types": ["authorization_code", "refresh_token"],
+                "scopes": ["read", "write"],
+                "owner_id": "507f1f77bcf86cd799439011"
+            }
+        }
+    )
+
+    id: Optional[str] = Field(default=None, alias="_id")
     name: str = Field(..., min_length=1, max_length=100)
     client_id: str = Field(..., description="OAuth2 Client ID (unique)")
     client_secret: str = Field(..., description="Hashed client secret")
@@ -38,21 +37,3 @@ class Application(BaseModel):
     owner_id: str = Field(..., description="User ID who owns this application")
     created_at: datetime = Field(default_factory=datetime.utcnow)
     updated_at: datetime = Field(default_factory=datetime.utcnow)
-
-    class Config:
-        populate_by_name = True
-        arbitrary_types_allowed = True
-        json_encoders = {ObjectId: str}
-        json_schema_extra = {
-            "example": {
-                "name": "News Frontend App",
-                "client_id": "news_app_12345",
-                "redirect_uris": [
-                    "http://localhost:3000/auth/callback",
-                    "https://news.example.com/auth/callback"
-                ],
-                "grant_types": ["authorization_code", "refresh_token"],
-                "scopes": ["read", "write"],
-                "owner_id": "507f1f77bcf86cd799439011"
-            }
-        }